Preparation And Application Of Kaolin-based Solid Acid Catalyst

Due to the enhancement of people’s environmental awareness and the demands of economic development, how to study and tap solid acid catalysts of low cost, high activity, reuse and less harmful to environment has become a hot research topic. Among the developed solid acid catalysts, SO₄^2-/M_xO_y solid acid catalyst has a good catalytic activity in a lot of chemical reactions. But it has some disadvantages, such as easy to deactivate, high cost and low surface area. Moreover, kaolin is widely used as catalyst supports owing to its low cost, eco-friendly and high cation exchange capacity. In order to improve the thermal stability of catalysts, reduce production cost and be separated easily from reaction system, three kinds of SO₄^2-/M_xO_y-kaolin catalysts were synthesized via adding kaolin to the support of SO₄^2-/M_xO_y solid acid in this paper. Catalytic performance of these catalysts was investigated for the synthesis of isoamyl acetate, hexyl butyrate and ethyl oleate, respectively. The main experimental process and results are as follows.（1） The solid acid catalyst SO₄^2-/ZrO₂-kaolin was synthesized. The structure and acidity of the catalyst were characterized by FT-IR, XRD, TG and NH₃-TPD. It was applied to esterification reaction of acetic acid and isoamyl alcohol for investigating its catalytic performance. Through single factor experiments, the suitable reaction conditions were obtained: entrainer cyclohexane 10mL, mass fraction of the catalyst in all reactants 3.1%, molar ratio of isoamyl alcohol to acetic acid 1.6:1 and reaction time 3h. The esterification rate reached 95.1% under the reaction condtions. After the catalyst was used five times, the esterification rate was 76.3%. The catalyst which had been used for five times could be regenerated by three methods.（2） The solid acid catalyst SO₄^2-/ZrO₂-SnO₂-kaolin（Ⅰ） was synthesized by introducing SnO₂ to the support of SO₄^2-/ZrO₂-kaolin catalyst, with higher activity than SO₄^2-/ZrO₂-kaolin for synthesis isoamyl acetate with acetic acid and isoamyl alcohol as reactants under the same conditions. The catalyst was characterized by FT-IR, XRD, TG and NH₃-TPD. Hexyl butyrate was synthesized by esterification of butyric acid and hexyl alcohol with the prepared catalyst. The esterification rate could reach 93.7% under conditions of entrainer cyclohexane 10 m L, mass fraction of the catalyst in all reactants 2.6%, molar ratio of hexyl alcohol to butyric acid 1.6:1 and reaction time 3 h. After the catalyst was used five times, the esterification rate was 65.0%. The catalyst which had been used for five times could be regenerated by three methods.（3） Ethyl oleate was synthesized from oleic acid and ethanol using SO₄^2-/ZrO₂-SnO₂-kaolin（Ⅰ） as catalyst. The esterification rate was 46.8% under conditions of catalyst dose 5.3% based on oleic acid, molar ratio of ethanol to oleic acid 7:1 and reaction time 8 h. Therefore, the effects of preparation conditions on the catalytic performance of SO₄^2-/ZrO₂-SnO₂-kaolin were investigated. The experiment results indicated that the appropriate conditions were as follows: sulfuric acid concentration for the impregnation 1.00 mol/L, mole ratio of Zr to Sn 1/3, calcination temperature 500℃, calcination time 3 h. And SO₄^2-/ZrO₂-SnO₂-kaolin（Ⅱ） was prepared under the above conditions. The effects of the reaction conditions on the esterification catalyzed by the catalyst were also studied. Through single factor experiments, the suitable reaction conditions were obtained: catalyst dose 7.1% based on oleic acid, molar ratio of ethanol to oleic acid 5:1 and reaction time 11h. Under the conditions, the esterification rate reached 83.5%. Moreover, the catalyst was reused for four times and the esterification rate could reach 68.2%.